The interface between the DCE and the
communication channel is currently defined only for voice grade analog
signalling as typically used with cable and radio channels. Corresponding
definitions for operation of optical fiber channels will be added to this
recommended practice when suitable standards for such channels become
available.

Channel interfaces for other types of
channels, e.g., power-line carrier, are not defined, as these are
implementationspecific. Voice-grade channel transmission characteristics are
required to be at least equal to those specified for unconditioned voice-grade
channels.

The DCE (i.e., modem) to voice-grade
channel interface should meet the following specifications:

Two modems, when interconnected by a
communication channel equivalent to an unconditioned voice grade channel,
should provide an end-to-end random bit error rate of less than 1 in 104 b.6
This performance, in conjunction with the security code and the limited message
length, ensures that the probability of acceptance of messages received in
error will be less than 1 in 1010, as specified in the IEEE Std C37.1-1987.

All
transmitters shall generate the selected data rate within a tolerance of ±
0.01% in accordance with CCITT Recommendations V.26 and V.27 bis [5] for the
two higher data rates above. This data rate tolerance also ensures adequate bit
synchronization accuracy for the longest permitted messages when using
asynchronous modems at the two lower data rates.

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